The effect of temperature on the resting tension of frog's muscle in hypertonic solutions.

1. It has long been known that the tension of a resting muscle rises when it is warmed and falls on cooling. It is shown here that treatment with hypertonic solution causes an alteration in this effect; the usual rise or fall of tension with warming or cooling is then preceded by a transient change in the opposite direction.2. The magnitude of the abnormal reversed phase does not depend in a simple, linear, manner on the temperature change. For instance, the effect for cooling from 20 to 0 degrees C is much greater than twice that for 10 to 0 degrees C.3. The results lead to the suggestion that the tension, in both normal and hypertonic muscle, comes from an active process. It is proposed that a temperature change operates by altering the concentration of an ;activating substance', and that the change of concentration becomes delayed by hypertonicity.